Extreme prematurity is the leading cause of infant morbidity and mortality in the United States, with over one third of all infant deaths and one half of cerebral palsy diagnoses attributed to prematurity. Respiratory failure represents the most common and challenging problem associated with extreme prematurity, as gas exchange in critically preterm neonates is impaired by structural and functional immaturity of the lungs. Advances in neonatal intensive care have achieved improved survival and pushed the limits of viability of preterm neonates to 22 to 24 weeks gestation, which marks the transition from the canalicular to the saccular phase of lung development. Although survival has become possible, there is still a high rate of chronic lung disease and other complications of organ immaturity, particularly in fetuses born prior to 28 weeks gestation. The development of a system that could support normal fetal growth and organ maturation for even a few weeks could significantly reduce the morbidity and mortality of extreme prematurity, and improve quality of life in survivors.
Premature birth may occur due to any one of a multitude of reasons. For example, premature birth may occur spontaneously due to preterm rupture of the membranes (PROM), structural uterine features such as shortened cervix, secondary to traumatic or infectious stimuli, or due to multiple gestation. Preterm labor and delivery is also frequently encountered in the context of fetoscopy or fetal surgery, where instrumentation of the uterus often stimulates uncontrolled labor despite maximal tocolytic therapy.
The 2010 CDC National Vital Statistics Report notes birth rates at a gestational age of less than 28 weeks in the United States over the past decade have remained stable at approximately 0.7%, or 30,000 births annually. Similarly, birth rates at gestational ages 28-32 weeks over the past decade in the United States have been stable at 1.2%, or 50,000 births annually. Patients with pulmonary hypoplasia secondary to congenital diaphragmatic hernia, oligohydramnios, or abdominal wall defects are also significant. The National Birth Defects Prevention Network reports an annual incidence of congenital diaphragmatic hernia between 0.9 to 5.8 per 10,000 live births in the United States, or approximately 375-2,500 births annually. The incidence of other causes of pulmonary hypoplasia is not well documented.
Respiratory failure remains the major challenge to survival in the critically premature infant. The development of an extrauterine system to support ongoing fetal growth and development would represent a changing paradigm in the management of such patients. The development of an “artificial placenta” has been the subject of investigation for over 50 years with little success. Previous attempts to achieve adequate oxygenation of the fetus in animal models have employed traditional extracorporeal membrane oxygenation (ECMO) with pump support, and have been limited by circulatory overload and cardiac failure in treated animals. The known systems have suffered from unacceptable complications, including: 1) progressive circulatory failure due to after-load or pre-load imbalance imposed on the fetal heart by oxygenator resistance or by circuits incorporating various pumps; and 2) contamination and fetal sepsis.
Accordingly, despite previous attempts to address the long-felt need for a system to support fetal growth and development for preterm fetuses, a solution has remained elusive.